The prior art smoke generator is described generally in U.S. Pat. No. 4,818,843, issued Apr. 4, 1989. Related patents include U.S. Pat. Nos.
4,764,660, issued Aug. 16, 1988, PA0 2,070,038, issued Feb. 9, 1937 PA0 4,318,397, issued Mar. 9, 1982 and PA0 4,114,022, issued Sep. 12, 1978.
The prior art smoke generator generally include a support housing, a liquid reservoir under pressure having a reservoir outlet pipe with a spray nozzle, a liquid pump connecting to the reservoir outlet pipe and having a pump outlet pipe, a coil heater connecting to the pump outlet pipe and having a heater outlet pipe extending to the exterior of the housing.
The U.S. Pat. No. 2,070,038 is directed to an apparatus for producing smoke which stays close to the ground. This is done by cooling the smoke with ice as the smoke leaves the conventional smoke generating apparatus. In the apparatus, the smoke making liquid is feed under pressure into the an air flow by means of a spray nozzle and a constricted pipe arrangement or venturi, is used to produce turbulence in the air flow. The pressure is necessary otherwise the smoke producing liquid can not pass through the spray nozzle. The use of spray nozzles have distinct disadvantages in that the nozzle tends to clog up and make continuous operation and maintenance very difficult. Further, because the smoke generating liquid is being supplied under pressure it is difficult to control the ratio of smoke generating liquid to air as the pressure is necessary to produce the spray. Still further, standard spray nozzles produce droplets that are too large for efficient, dry smoke production. Efficient spray nozzles require compressed air sources which introduce excessive cooling.